As you know, a lot of request (images, scripts, AJAX, etc.) are send when loading a single page. So I need to get all those request and inspect them.
So the question
The best you can get in your app is the WebViewClient.shouldInterceptRequest method, but that only has the URL. You currently can't get any of the things you've listed.
WebViewClient.shouldInterceptRequest
For debugging you can use Chrome DevTools if you're using Android 4.4.